Investigating the influence of the constituent materials on the performance of periodic piezoelectric composite arrays

This paper describes a theoretical investigation into the influence of the constituent materials on periodic composite array transducer performance. A finite element (FE) model, configured in PZFlex, is used to analyze the performance of a wedge coupled array transducer operating into a steel component. Here, the improvements offered by new single crystal piezoelectric materials are compared to standard PZT‐based configurations. In addition, new passive polymer materials, possessing low longitudinal loss and high shear loss, are evaluated for their potential to significantly reduce inter‐element mechanical cross talk. The FE results illustrate the potential for the next generation of array transducers incorporating these new materials and this is highlighted in the A‐scan predictions from simulated defects

Application of pulsed power generated high power ultrasound to waste comminution and the recovery of metals

The disposal of waste materials is an increasing burden on industry across the world. In order to address this problem, the development of viable technologies and recycling paths is required. Often it is necessary to process waste to reduce its size (comminution) or to allow the recovery of high value components entrapped in waste. This paper describes the application of high power ultrasound (HPU), generated using pulsed power techniques, to two waste products: glass and stainless steel slag

High power ultrasound for acoustic source applications

High Power Ultrasound (HPU) can be generated by the application of Pulsed Power Technology to produce acoustic waves of high power and bandwidth. A study was conducted into the variation of the amplitude and frequency content of the acoustic signal with the applied voltage, pulse energy and electrode separation. Measurements indicate that, for a given electrode separation, whilst there is some increase in the amplitude of the detected acoustic emission with an increase in the electrical pulse energy it is only a modest effect. For a given pulse energy a considerably greater increase in the acoustic signal is observed when the distance between the electrodes is extended - thereby increasing the size of the signal source. The maximum amplitude of the detected signal approximately varies as the electrode separation to the power of (2)/(3). At large separations the delay time between the application of the voltage pulse and the breakdown of the water is considerable thus allowing energy loss through ionic conduction in the water

Generation of high power ultrasound by spark discharges in water

It is impractical to achieve the desired combination of power and bandwidth from conventional electromechanical acoustic sources. However, these characteristics can be achieved by the use of pulsed power technology to generate high-power ultrasound (HPU). High-voltage pulses induce the electrical breakdown of water and the resulting bubble formation and collapse produce acoustic waves of high power and frequency. The dynamics of spark generated bubbles are formulated to predict the development of the bubble radius with time and an experimental system to produce a consistent source of spherically symmetric HPU acoustic waves is described. Pressure pulses due to both bubble formation and collapse were detected and, although their relative amplitudes varied, their frequency spectra did not differ significantly. The amplitude of the acoustic output rises sharply for applied pulse energies up to /spl sim/25 J but the effect saturates indicating little gain and poor efficiency by using high-energy pulses. Variation of the source topology in the form of the electrode separation was found to be the most important factor in the acoustic output. The detected HPU increased as the source became larger but as the two-thirds power of the electrode separation, thereby showing progressively diminishing enhancement. The frequency content of the acoustic signal did not appear to vary with either applied pulse energy or the electrode separation

Plasma channel microhole drilling technology

With growing economic and environmental pressures, oil companies seek ways to increase the oil recovery from every well. Re-entry drilling of horizontal sidetracks from existing wells and multilateral drilling for new wells are techniques which help to achieve that. However, new approaches are needed to reduce the cost and to improve efficiency of rotary drilling methods used for these purposes. This research aims to develop a new plasma channel drilling (PCD) method for drilling of small diameter holes (3.5-15 cm) for sidetrack creation and multilateral drilling. The method relies upon the use of the energy of impulse plasma discharges which are formed inside rock formation ahead of the drill position. Repeated formation of the plasma channel results in an effective and controlled drilling action. Plasma channel drills developed at Strathclyde University are able to cut clearly defined circular holes in sandstone with a speed of up to 16 cm/min. Plasma channel drilling has the potential to significantly increase the lifetime of oil wells and would dramatically reduce the cost of exploration drilling and subsurface data acquisition. PCD technology can also be a cost-effective and practical solution for other applications such as mineral mining, water boring, scale removal where micro-hole drilling is essential

Enhanced flexibility and performance from piezocomposite 2D array with a dual-polymer phase improved structure

This paper describes an improved conformable composite array structure, for use in the NDE of irregular surfaces featuring efficient piezocomposite elements as the active array elements and soft polymer phase channels between elements. As each array element is in principle an individual piezocomposite, this device has been named a Composite Element Composite Array Transducer (CECAT). Finite Element (FE) virtual prototyping work identified two possible arrangements for the active phase incorporating either a periodic 1-3 composite or a random piezoceramic fibre structure with examples of both presented. Theoretical simulations and experimental measurements of impedance, surface displacement and mechanical cross talk demonstrate good correlation at an operational frequency of 2 MHz. The CECAT shows superior flexibility and acoustic characteristics over similar piezo-platelet arrangements and comparable sensitivity and bandwidth with a regular 1-3 composite. Enhancement of the piezoelectric performance of each array element is possible through implementation of a dual polymer passive phase configuration

Influence of gamma radiation on the properties of polyethylenectapthalate (PEN)

Foil samples of polyethylenenapthalate, 25 mum thick have been subjected to radiation doses of 26.5 and 158.4 kGy from a Co-60 source to promote ageing. The current transients produced by the application and removal of a DC voltage to the samples were measured over an extended period of time. Peaks in both the charging and discharge currents were observed whose positions were dependent on both temperature and radiation dose. Activation energies were obtained from isochronal charging currents and from the frequency domain. These showed a dose dependence. Curve fitting to the initial discharge transient and to the dielectric loss peak in the frequency domain indicated that the ageing had not produced changes in the type of loss mechanisms. A linear relationship was found between the received dose and the dieelctric loss peak position

The low frequency response of styrene butylene rubber (SBR)

Charging and discharging currents due to the application of a step voltage to styrene butylene rubber (SBR) 50 mum thick were measured for a 1.27 x 10(5) s as a function of temperature from 30 to 120degreesC. Activation energies were derived from the isocronal measurements of the charging currents for two distinct temperature regions. Transformation of the discharging current to the frequency domain identified two loss peaks. An activation energy was determined for the higher frequency peak. Curve fitting allowed the resolution of the lower frequency peak and the determination of the temperature dependence of the fitted parameter

Exploring the advantages of a random 1-3 connectivity piezocomposites structure incorporating piezoelectric fibres as the active element

This paper describes the use of piezoelectric ceramic fibres (PZT5A) for the fabrication of 1-3 composite transducers. Importantly, extensive FE analysis, using the PZFlex code, of these devices has been undertaken with complete 3D models utilised to reflect the random nature of the device structure. The manufacturing process is based on the place-and-fill method. A fibre composite block is produced, from which it is then possible to slice a number of layers of piezoelectric material with a thickness corresponding to the desired frequency of operation. These layers have electrodes applied and are then poled. Electrical impedance profiles of each device demonstrate excellent unimodal behaviour at the thickness resonance frequency, and show excellent correspondence with the FE models. Moreover, these devices possess high electromechanical coupling coefficients (kt > 0.65) for a ceramic volume fraction of 50% and a medium-set polymer (CIBA GEIGY CY221-HY956). Laser vibrometry scans of transducer surface motion corroborate the FE predictions of average uniform surface displacement notwithstanding local variations due to the random nature of the microstructure. Experimental pulse-echo assessments, when operating into a water load, demonstrate comparable sensitivity and bandwidth characteristics between a random fibre and conventional 1-3 composite, with similar specification

Evidence of nuclear membrane damage in yeast cells treated with pulsed electric fields

The application of pulsed electric fields (PEF) as a process in the treatment of liquid foodstuff, although not fully understood, appears to have significant potential. This treatment technology represents a promising nonthermal technique that may supplement or replace conventional pasteurisation methods for some applications. The advantages of such an electrotechnology include the potential retention of fresh-food characteristics and organoleptic qualities such as flavour, aroma, and texture. Pulsed electric field inactivation of microorganisms is generally thought to be caused by irreversible structural changes in the cellular plasma membrane resulting in swelling or shrinkage and finally lysis of the cell. Previous evidence of this external membrane damage has not established what damage, if any, is caused by PEF treatment on the internal structure of the cell. This investigation using laser scanning transmission microscopy of the spoilage yeast Zygosaccharomyces bailii after PEF treatment shows evidence of internal damage to the nuclear membrane. It has been reported that electric field rise times in the 1-100ns range are required for intracellular electroporation. The laser images indicate that this range must be more extensive than previously reported since with the rise time of ∼160ns extensive nuclear membrane damage has been caused to the yeast cells. Such damage, in combination with plasma membrane damage, could contribute to the inactivation of Z. bailii by PEF